Ray Tracing and Global Illumination

Ray tracing is a significant field of computer graphics used for rendering highly realistic imagery for computer animated films, scientific data visualization, architectural and engineering designs. Challenges include rendering imagery of the highest quality indistinguishable from reality, but also to do so in a cost and time-effective way. The group in Swansea has concentrated on both aspects.

New methods significantly improve the visual quality of global illumination at reduced rendering cost by pre-processing the photon map. In these techniques, the source photon positions are relaxed or capacity constrained. This greatly reduces the variance of the resulting images. Bias was also greatly reduced by constraining the relaxation process in the vicinity of edges of photon density. The overall result is that fewer photons need to be considered in the density estimation phase, resulting in a significantly faster rendering time, but still achieving higher quality images (due to the reduced variance). This is a significant result for global illumination, and the resulting technique applied to the leaf image won the cover competition for the journal Computer Graphics Forum (2009)

The first application of divide-and-conquer to ray tracing led to a new fundamental data structure-less approach for ray intersection. Since ray-tracing became widespread 30 years ago, all approaches have used algorithms based on pre-computed data structures to improve the speed of the algorithm. Divide-and-conquer ray tracing is a radical departure from all previous work, simplifying software engineering by allowing deterministic memory consumption and providing state-of-the-art performances. The new approach is faster than other techniques and is a significant advance when used with massive and dynamic scenes. This approach is implemented inside a free of charge Graphics library available at www.directtrace.org.

There are a great number of other contributions in the area. Other work combined progressive photon mapping for caustic light paths and path tracing into one framework for creating low variance and low bias realistic images. New data structures for ray tracing have been proposed such as Row Tracing, Restricted BSP-trees, and Hierarchical Photon Maps. Three dimensional caricature style renderings were created from artist capture styles and a single subject photo.

Three-dimensional emissive displays create “holographic” like images that can be viewed from any vantage point around the device. A problem with these displays is that they produce X-ray like transparent objects. A major contribution has been to create 4D light fields from 3D objects to enable opaque fully shaded views of 3D objects on these devices.